Not applicable.
This invention relates to tree felling heads, and in particular to the construction of a tooth and a disc saw blade for such heads.
Four-sided rotatable teeth for disc saw blades of tree felling heads are known, for example, from U.S. Pat. Nos. 5,579,674; 5,647,263; and 5,813,308. With such teeth, one edge of the tooth is positioned radially outermost from the rotary axis of the blade to cut a kerf in a standing tree. The tooth is oriented on the blade with one of the sides on the outside of the blade so that the cutting edge is substantially vertical in the cutting position of the blade, as the blade is advanced through a tree. The outside cutting edge forms the kerf by chiseling off the working (vertical) surface of the kerf, and chips from the cutting operation flow along the attack face of the tooth for evacuation from the kerf. When the outside edge becomes dull, the tooth is rotated about its longitudinal axis and resecured to present a sharper edge in the outermost position for cutting. When all edges become dull, the tooth is replaced or reconditioned.
With such teeth, two of the sides of the tooth are in a substantially horizontal plane, one of the horizontal sides being on the top side of the tooth and the other horizontal side being on the bottom side of the tooth. The top side of the tooth is in close proximity or contact with the top side of the kerf (on the tree trunk) and the bottom side of the tooth is in close proximity or contact with the lower side of the kerf (on the top of the stump). This close proximity or contact results in a certain amount of wear along the top side edge and bottom side edge of the tooth during a cutting operation. Of course, the outermost edge also wears, since it does most of the cutting. Thus, with four-sided teeth, edges and tips of the teeth which are not forming the kerf are being worn during the cutting operation, with the effect of inefficiently reducing the useful life of the tooth.
The present invention provides a disc saw blade which has multi-tip rotatable teeth in which only one tip of each tooth is exposed outside of the plane of the blade to cut a kerf in a tree. Thereby, only one of the tips of each tooth wears in each position of the teeth, and the other tips are protected in each position.
In a preferred form, each tooth has three cutting tips, with one tip of each tooth subjected to wear during the cutting operation and the other two protected within the plane of the blade. The two idle cutting tips are below the worn position of the active cutting tip, and therefore, do not engage the kerf until they are rotated to a cutting position.
The invention also provides a tooth in which one tooth size can be used on blades of various kerf sizes. Smaller teeth allow for a smaller gullet which permits the use of a butt plate which extends out further (i.e., larger in radius) to support cut trees on.
Preferably, locating surfaces on the tooth and disc are angled up or down, preferably at 45xc2x0, to locate each tooth with a tip exposed to cut either the upper or lower surface of the kerf. Such surfaces can counteract vertical, horizontal and tangential loads and prevent rotation of the teeth relative to the disc, to help relieve the other parts of the tooth mount. In addition, at least one of the locating surfaces can be angled to exert a preload force on the tooth as the two surfaces are drawn together.
In another preferred aspect, the side surfaces of the teeth which define the cutting tips diverge from one another at an angle of greater than 60xc2x0 to an apex of each side surface. This adds tooth material at the tip to slow down the wear of the exposed tip.
In another preferred form, the axis of each tooth is angled either up or down relative to the cutting planes, to position one of the cutting tips of each tooth in either the upper or the lower cutting plane. This enables using smaller teeth, which results in advantages in the cost of the teeth, the size of the butt plate (larger in area and thicker for a given size tooth) and the cutting power requirement.
The foregoing and other objects and advantages of the invention will appear in the detailed description which follows. In the description, reference is made to the accompanying drawings which illustrate a preferred embodiment of the invention.